There is a difference between "hard" and "brittle".
"...many people expect a diamond to be unbreakable. This is not true. A diamond's crystal structure has "hard" and "soft" directions. A blow of sufficient force, in a very exact direction, can crack, chip, split or even shatter a diamond."
Kakuzu is not a bad match up for Sasuke - on the contrary, Sasuke is a bad match up for Kakuzu. Kakuzu's Doton skin has shown itself to be very weak against Raitons. Sasuke is a Raiton pro. Chidori Senbon ftw.